A drive circuit for an Organic Light-Emitting Diode (OLED) in the prior art is shown in FIG. 1. A Thin Film transistor (TFT) is directly driven by a grayscale voltage VDATA (i.e. voltage supplied by a data line, which is a voltage of the data signal) and different currents are generated according to various VDATA to lighten an OLED device.
A current flowing through a drive transistor of the OLED device (i.e. the TFT T1) may be obtained by a following equation:
      I    =                  1        2            ⁢                        μ          n                ·        Cox        ·                  W          L                ·                              (                                          V                GS                            -                              V                th                                      )                    2                      ,
in which, μn is a channel carrier mobility, Cox is a capacitor of a gate oxide layer of the transistor,
  W  Lis an aspect ratio of the channel of the transistor, and it may be approximated that VGS=VDATA−VOLED, Vth represents a threshold voltage for the TFT transistor T1.
The current flowing through the OLED device is indicated as follows:
      I    OLED    =            1      2        ⁢                  μ        n            ·      Cox      ·              W        L            ·                                    (                                          V                DATA                            -                              V                OLED                            -                              V                th                                      )                    2                .            
A TFT transistor T2 in FIG. 1 functions as a switch control transistor, the on/off of which is controlled by a voltage VSCAN of a line scanning signal; and the TFT transistor T1 in FIG. 1 is the drive transistor. When a scan line is on, the data signal of VDATA of an external circuit is stored in a storage capacitor (Cs) via the switch transistor T2. Such a data signal controls an amount of turned on current of the drive transistor TFT and also determine a grayscale of the OLED. When the scan line is off, a voltage stored in the capacitor Cs may keep the drive TFT in a turned on state.
In an actual display panel, due to mismatch at different positions caused by process offset, the threshold voltages of the TFT drive transistor T1 in the panel change, so that an operation voltage VOLED generated by the current flowing through the OLED lighting device also changes. Thus, there is inaccuracy in the current flowing through the OLED lighting device, so that uneven brightness occurs in the screen.
To sum up, the drive circuit for the OLED in the prior art is influenced by instable factors of the drive transistor and leads to inaccuracy of the current flowing through the OLED, so that the brightness in the whole screen is uneven.